1. Field of the Invention
The present invention relates to a surface emitting light source and projection display device using the same. Particularly, the present invention relates to the surface emitting light and the projection display device which have semiconductor light emitting units which emit lights having a plurality of colors.
2. Discussion of the Related Art
Currently, a high demand exists for display devices that are capable of producing large, high quality images. Representative examples of display devices capable of producing large images include direct-view type liquid crystal displays (LCD), plasma displays, projectors and the like.
Conventional projection display devices typically filter light having the necessary wavelength with a R(red)/G(green)/B(blue) color wheel filter. Hence, conventional projection display devices typically have poor light efficiency and limited color reproduction. The rotating motion of a color wheel often introduces a noise problem. Furthermore, the wear and tear of a color wheel often limits the duration of use. Finally, since only one-third of incident white light is transmitted, efficiency of light use is also lowered.
Meanwhile, a light emitting diode (LED), which is a device that emits light when electrically biased in the forward direction, requires low power and is widely used when only a small light source is needed, and for display devices. LEDs emit narrow-spectrum light, which provides excellent color reproduction performance. Because LEDs have relatively small power consumption, LEDs are capable of being substituted for the lamp of a conventional projection display device.
As emitting efficiency of LEDs has increased, LEDs are being used in new applications that have previously been reserved for other types of light sources that have traditionally produced higher levels of brightness. However, higher output power is still needed before an LED can reliably be used as the light source of a projection display device. Since it is insufficient for one LED to be used as the light source of the projection display device, several LEDs are often combined for use as a surface emitting light source.
Where several combined LEDs are used as a surface emitting light source, the number of LEDs that may be used is limited because LEDs are large in size in comparison to many display devices, such as a digital micro-mirror device (DMD). Because the number of LEDs that may be included as a surface emitting light source is small, it is difficult to obtain a high level of light output. Moreover, the spacing that necessarily exists between LEDs is typically too wide to provide a uniform distribution of light.
When LEDs are employed for a large-size screen such as an outdoor multi-signboard, or for a large-sized screen that is meant to be viewed from a distance, the LEDs have no problem in displaying an image. On the other hand, when LEDs are used as a light source of a small display device or on a small screen meant to be viewed at a close distance, brightness uniformity of the screen is degraded due to the lack of uniformity of the light distribution. Furthermore, since a drive electrode line needs to be connected to each LED, a connection circuit line becomes complicated.
A single panel type DMD projector using an LED surface emitting light source typically synthesizes R, G and B lights and then separates the synthesized lights. Hence, the related art single panel type DMD projector typically requires a complicated optical system. Specifically, since a cross-sectional area of light increases in proportion to the distance from an LED light source due to a big angle of emission, the accompanying optical system, including a lens, prism, and the like, also usually suffers from increasing size. Consequently, the overall size of the projection system also increases.